1. Field of the Invention
The present invention relates to multi-band switch modules which can transmit and receive signals in a plurality of frequency bands and which are mounted in portable terminal apparatuses.
2. Description of the Related Art
In recent years, in the area of cellular phones, smooth voice communication or data transmission/reception has become difficult when only a single frequency band is used due to the increasing number of users. Thus, cellular phones have been produced to support multiple bands so that a single cellular phone can handle a plurality of frequency bands.
In this case, one method of supporting a plurality of frequency bands is to provide individual circuits for the respective frequency bands in a cellular phone. However, since this method makes it difficult to reduce the size of a cellular phone, it is preferable to form the circuits such that a single component for a common function is shared by all the circuits. Thus, a technique has been proposed in which all signals in different frequency bands are transmitted and received together using a common antenna and are separated for each frequency band by a switch module including a demultiplexer circuit and a switch circuit.
In such a switch module, a plurality of mounting electrodes is provided on, for example, one main surface of a wiring substrate, on which the switch module is provided, for input/output of a signal from/to a mother substrate. Since a reduction in the size of a switch module is required in accordance with the reduction in the size of cellular phones, there is a tendency for the area of the main surface of the wiring substrate to be decreased. In this case, the distance between the mounting electrodes needs to be decreased, such that an influence from mutual interference among signals, i.e., mutual leakage of signals among the mounting electrodes used for input/output of RF signals, is increased, which may cause a failure, such as a communication failure.
Thus, referring to FIG. 10, a switch module 200 has been proposed in which, among a plurality of mounting electrodes 202 provided on a wiring substrate 201, the mounting electrodes 202 used for input/output of RF signals are arranged so as to be sandwiched between ground electrodes 203 (refer to, for example, paragraph 0051 and FIG. 3 of Japanese Unexamined Patent Application Publication No. 2002-64301).
The switch module 200, which is a module that supports three different communication systems, includes a demultiplexer and a plurality of switch circuits for demultiplexing signals of the three transmission/reception systems and a plurality of low pass filters provided in transmission/reception paths. A diode 204, a chip capacitor 205, and a chip resistor 206, which are components of the circuits, are mounted on the wiring substrate 201, and a plurality of the mounting electrodes 202 used for input/output of the RF signals are provided along the periphery of the wiring substrate 201. Each of the plurality of the mounting electrodes 202 is arranged so as to be sandwiched between the ground electrodes 203.
In this manner, the RF signals leaking from the mounting electrodes 202 used for input/output of the RF signals are conducted to the ground electrodes 203 and, thus, mutual interference among the RF signals at the mounting electrodes 202 is suppressed, such that isolation characteristics of the mounting electrodes 202 can be improved.
However, due to further demand for a reduction in the size of the switch module 200, it has become difficult to ensure a space to provide the ground electrodes 203 between the mounting electrodes 202 used for input/output of the RF signals whose mutual interference is to be suppressed. Methods of ensuring a space for arranging the ground electrodes 203 include reducing the areas in which the mounting electrodes 202 are provided and employing a smaller spacing between the mounting electrodes 202. However, since mounting of the switch module 200 becomes difficult and short circuiting between the mounting electrodes 202 may occur at the time of mounting, a technique, other than the above-mentioned methods, of suppressing mutual interference between the RF signals at the mounting electrodes 202 and achieving a reduction in the size of the switch module 200 has been desired.